Divisible electric conductor



Oct. 17, '1939. H. H; WERMINE 2,176,233

DIVISIBLE ELECTRIC CONDUCTOR Original Filed Jan. 18, 1936 JO 0 I 2 Patented Oct. 17, 1939 UNITED STATES PATENT OFFICE DIVISIBLE ELECTRIC CONDUCTOR Hugo H. Wermine, Villa Park, Ill., assignor to Belden Manufacturing Company, Chicago, 111.,

a corporation of Illinois Original application January 18, .1936, Serial No.

Divided'and this application March 25,

1938, Serial No. 197,997

4 Claims.

7 application, Serial No. 753,657, filed November 9,

This invention relates to improvements in electrical conductors and more particularly to duplex conductors of the type typified by socalled lamp cord which is now available on the market in the form of a more or less transversely oval-shaped rubber strip in which the conductors are embedded in predetermined spaced. relation to each other. Such lamp cord is available in various colors to suit the requirements of different situations and it is characterized by the absence therefrom of the more or less conventional braided fabric covering. Such fabric coverings or sheaths, as heretofore commonly used, have been more or less necessary for the purpose of binding separate insulated conductors together in a single cable or lamp cord, and such braided or like sheaths have been a frequent source of annoyance because of the tendency of the fabric sheath to fray at the ends of the cord or at intermediate points when the braided fabric is worn.

The present type of rubber-covered lamp cord embodies a pair of conductors, either with or without servings of cotton thread or the like, and a one-piece or unitary coating of rubber or similar insulation materiaL. Such cord may be manufactured very economically and at low cost by the simple operation of extruding suitable rubber compound around properly spaced and guided conductor wires. However, one of the difficulties experienced in employing such rubber covered duplex conductor is that it is very diflicult to split or divide a length of the duplex conductor into separate insulation covered wires, for example, at the end of a length of the cable for the purpose of connecting the wires to the terminals of a lamp socket, connector plug or other electrical device. In splitting such conductor it is found that the line of division has a very noticeable tendency to migrate from the desired line of separation toward one or the other of the conductor wires with the resultant baring of portions of the wire which it is preferred to keep covered.

It is the object of the present invention to provide a duplex or multi-wired electrical conductor cable or cord embodying an arrangement whereby separation of the wires with the retention thereon of an adequate covering of insulation material is facilitated.

Other objects and advantages of theinvention will be understood by reference to the following specification and accompanying drawing wherein there are illustrated three specific forms of electric conductor cable embodying the invention, and portions of apparatus for producing the improved cable.

In the drawing:

Figure 1 is a fragmentary illustration in section of an extruding head adapted to produce lamp cord embodyingthe invention;

Figures 2 and 3 are sections on the lines 2--2 and 3-3, respectively of Figure 1.

Figure 4 is a section on the line 4-4 of Figure. 1, through the cable produced by the apparatus shown in Figure 1;

Figure 5. is a perspective of a length of cable produced by the apparatus shown in Figure 1;

Figure 6 is a section corresponding to Figure 3 but showing a modified arrangement;

Figure '7 is a fragmentary perspective of an element of apparatus used in producing the cable form represented in Figure 6;

Figure 8 is a cross section also similar to Figure 3, but showing another arrangement embodying the invention, and

Figure 9 is a perspective similar to Figure 7, but showing the form of a portion of the apparatus employed in producing the arrangement illustrated in Figure 8.

Referring now to the drawing, the form of lamp cord illustrated in Figures 4 and 5 embodies a pair of electric wires l0, l0, which are preferably, although not necessarily, of stranded construction so as to be flexible to meet the usual requirements of so-called lamp cord. The wires l0, ID, are disposed in substantially parallel'but spaced relation and they are enclosed in a jacket or shield I l of rubber or other suitable insulation material which serves to maintain the conductors in their predetermined spaced parallel relation.

The shield or jacket of insulation material is formed integrally about the conductor wires and is provided with a pair of chambers l2, l2, which are spaced transversely of the pla ne of the wires l0, l0, and disposed approximately midway or equi-distantly spaced from said wires. The chambers l2, l2, extend longitudinally of the cable and serve to guide the splitting of the insulating sheath intermediate the wires IO, N), as indicated at I3 in Figure 5. The cross sectional size of the chambers l2, l2, may be varied considerably, but it is preferable that they be of such materially greater than, and preferably less than, the smallest transverse dimension of the rubber insulation material in any plane extending longitudinally of and through either wire.

For forming the described cable, the wires"), III, are guided through suitably spaced apertures in a tip I4 carried by the tip-supporting element I5 of a rubber or like material extruding head. The cross sectional shape of the rubberjacket is determined by the shape of a die opening I6 in a die piece I1 which is supported by means of a nut orthe like indicated at I8 and carried by the main casing I9 of the extruding head. The tipsupporting element I5 is also carried by the main casing or housing I9 through the agency of a sleeve which is suitably locked in place in the housing. As indicated, the tip holder I5 is. adjustable forwardly and rearwardly relative to the die IT, in this instance being mounted through the agencyof screw-threading 2I in the sleeve 20.

Suitable uncured or unvulcanized plastic rubber or similar composition Ila is forced under pressure through the die opening I6 around the spaced conductors I 0, I0, which are guided through said die opening by the tip I4 as clearly indicated'in Figure 1 of the drawing. The means for feeding the insulating composition Ila under pressure may be a conventional screw press or ranged in various degrees of spaced relationship and in some instances they may even be disposed in contact with, eachv other. It will be apparent that the presence of the projecting pins 22, 22, will result in the formation of the chambers I2, I2, in the insulating material intermediate the wires.

The projecting pins 22, 22, preferably project substantially beyond the outlet e'nd'of the die opening I6 as indicated in the drawing, it being found that the production of the cable may then be practiced without maintaining any finely adjusted relationship between the wire guiding tip I4 and the inner end of the die I1.

It is noted that within the die opening I6 there. is considerable pressure on the insulating composition and that such pressure probably has the effect of more or less compressing the rubber-like insulation material. When the rubber emerges from the die opening I6 it may expand slightly, so that there will be no tendency for the composition to close around the ends of the pins 22, 22. However, the length of the pins'may be considerably varied. In fact, they may be short enough to terminate within the die opening, but

in that event it is advantageousto feed the in in some instances, tend to close up so as to appear more like elongated, slightly open slits as indicated in Figure 4, such closing being perhaps due to the tendency of the insulating composition to expand upon issuancefrom the die. Whether or not the chambers thus formed contain either air or some other fluid has not been ascertained. They may contain air, which may possibly find its way thereinto from the front end of the cable as it' issues from the extruding head. However, it appears likely that the chambers contain certain fluids in the form of gases produced as an incident to the vulcanizing step.

The extent or degree of opening maintained may be varied and it may be controlled by suitably regulating the pressure under which the insulating material is fed into and through the die, by suitably adjusting the length of the pin or pins which produce the openings, and by regulating or maintaining the consistency of the insulation material as required to secure the desired open condition of the openings. It is preferable that the openings be permitted to, or so shaped that they occupy only a small cross-sectional area. The area of the opening is not of material importance, except in so far as it bears on the cross-sectional size of the finished conductor. In order that the latter may be maintained as small as practicable, it is desirable that the openings be permitted or caused to close up to present the slit-like appearance shown in Figure 4. In this way, the crosssectional size of the finished conductor is maintained at a minimum while affording a maximum thickness of insulation around each wire.

In Figures 6 and 7, there is illustrated the pro duction of another arrangement of conductor embodying the invention. In this form only one pin designated 22a is carried by the wire guiding tip I4. The pin 22a is located intermediate the two wires ID, ID in the plane thereof and serves to produce only a single opening or chamber in the conductor. Such single opening obviously serves the purpose of a pair of openings or chambers as above explained and provides a stronger bond between the respective halves of the rubber jacket around the respective conductor wires I0, III. Conductor wire embodying this form of the invention may be somewhat more diflicult to separate than the form illustrated in Figures 4 and 5, and in some instances such increased strength may be desirable.

In Figures 8 and 9, another arrangement is shown. In this arrangement, a single chamber forming pin 22b is employed, the pin in this instance being somewhat hour-glass in cross section. The cross sectional shape ,of the pin 22b is such that it embodies an elongated dimension extending transversely of the plane of the wire Ill, I0, to form an opening or chamber in the insulation jacket, which opening extends beyond the oppositesides of the pair of wires III, II). In this arrangement a weaker bond is provided between the opposite halves of the insulation material around the respective conductors so that separation of the cable into independent insulation covered wires is facilitated. The hour-glass shape of opening is also advantageous in that the central portions of insulating material indicated at 23, 23 on opposite sides of the hour-glass shaped opening may abut each other to thereby present complete closing of the opening portions adjacent the widened ends of the opening. During the process of vulcanization, such abutting portions may be more or less united but the joint so formed is comparatively weak and .does not hinder separation of the wires in the manner explained. p

It will, of course, be apparent that the formation of chambers as above explained may be practiced in connection with conductor cables of more than two wires so as to permit separation of such wires, for example in a three-wire cable. Also the wires of a multi-wired cable may be located all in a common plane or they may be arranged concentrically about a predetermined axis or any other relationship.

Other changes may be made in the conductor structure, in the method of producing the same and in the apparatus therefor, without departing from the spirit of the invention, the scope of which should be determined by reference to the following claims, the same being construed as broadly as possible consistent with the state of the art.

I claim:

1. Divisible duplex electric conductor comprising a pair of spaced conductor wires and a unitary insulation sheath of resilient material, said insulation sheath being provided with a pair of voids located in a predetermined plane intermediate, extending longitudinally of, and spaced from said wires, said voids serving to reduce the area of insulation sheath in said predetermined plane to facilitate and guide division of the duplex conductor by tearing said sheath in spaced relation to the wires.

2. Divisible duplex electric conductor comprising a pair of spaced conductor wires and a unitary insulation sheath of resilient material, said insulation sheath being provided with an internal void located in a predetermined plane intermediate, extending longitudinally of, and. spaced from said wires, said void serving to reduce the area of the insulation sheath in said predetermined plane to facilitate and guide division of the duplex conductor bytearing said sheath in spaced relation to the wires.

3. Divisible duplex electric conductor comprising a pair of spaced wires and a unitary insulation sheath of resilient material, said sheath 4. Divisible duplex electric conductor com prising a pair of spaced conductor wires and an insulation sheath of resilient material, said insulation sheath being provided with an internal void located in a predetermined plane intermediate, extending longitudinally of, and spaced from said wires, said void serving to reduce the area of the insulation sheath in said predetermined plane to facilitate and guide division of the duplex conductor by tearing said sheath in spaced relation to the wires.

HUGO H. WERMINE. 

